Process for preparing steels and alloys for rolling



Patented May 5, 1953 PROCESS FOR PREPARING STEELS AND ALLOYS FOR ROLLING William Oakley Binder, Niagara Falls, N. Y., assignor to Union Carbide and Carbon Corporation, a corporation of New York No Drawing. Application January 8, 1952,

I Serial No. 265,545

This invention relates to a method for removing, surface imperfections from steels and alloys and is particularly useful for treating the surfaces of these materials prior to a shaping ope-ration such as rolling.

Ingots, slabs; billets, castings and the like usually have surfaces that are unsuitable in finished articles. If the metal is to be rolled, some of the surface imperfections are eliminated during normal rolling, but others are so serious that they detrimentally affect the quality of the finis hed article unless they are removed before the final rolling. The more objectionable surface imperfections are attributable, for example, to seams, scabs, and blowholes. conventionally, these more objectionable imperfections are removed by such operations as grinding and chipping the metal, both of which are tedious, laborious and wasteful operations. Castings also often have undesirable surface imperfections and these too are eliminated conventionally by removing part of the metal of the casting by grinding, chipping or the like.

It is an object of the invention to provide a method for removing imperfections from the surfaces of bodies of steel or other alloys. v

Another object of the invention is to provide a method for eliminating defects in the surfaces of semifinished articles of steel and other alloys which defects can impair finished products rolled from the semifinished articles.

. The objects of the invention are accomplished by heating an article of steel or alloy to a temperature of between 700 C. and 120050. and exposing the article while it is in that temperature range to a gaseous sulfur compound as described below. Best results have been obtained with treatments at temperatures of from 950 C. to 1050 C. During this treatment the metal is attacked generally and a loose scale'forms on its surface. This scale can be easily removed, for example by chipping or sandblasting, the work being required to remove this loose scale being much less than that required for chipping or sandblasting the metal itself. Under the scale is a smooth surface relatively free of imperfections. If the treatment is continued long enough, the injurious and undesirable imperfections on the surface are eliminated.

Thesulfur compounds used in the process must be those which are normally gaseous at a temperature of between 700 C. and 1200 C., and preferably at a temperature of about 700 C. They must also be ones which will dissociate at a temperature of between 7003C. and 1200 C. in the presence of the steel or alloy being treated 12 Claims. (Cl. 134-4) to make sulfur available for reaction with the steel or alloy. Sulfur containing compounds which dissociate to free oxygen should be avoided since oxygen tends to attack the metals intergranularly rather than generally. The preferred compound is hydrogen sulfide. Examples of other compounds that can be used are sulfur dichloride, sulfur tetrachloride, ammonium sulfide, and carbon bisulfide. With some of these compounds certain incidental effects such as mild carb-urizing and nitriding are obtained.

It has been found that when certain alloys are treated at temperatures above about 850 C. for times suflicient to remove relatively deep surface imperfections, two scales are formed. For example, when surface imperfections are removed according to the invention from alloys containing nickel, cobalt and more than about 18% chromium by holding these materials at about 1000 C. in a stream of hydrogen sulfide, an inner scale may be formed in addition to the loose scale mentioned above. This inner scale is thin and adheres tightly to the treated metal so that it cannot be removed as readily by sandblasting and chipping as the loose outer scale. This inner scale may detrimentally affect the treated metal if it is not removed. For example, if the metal is to be rolled further, the inner scale tends to penetrate the metal intergranularly and cause shallow surface cracking. The inner scale also tends to diminish the resistance of the metal to corrosive attack.

The inner scale may be removed by again treating the metal with the gaseous sulfur compound, in this instance hydrogen sulfide, at a temperature of from 700 C. to 850 C. A temperature of 800 C. is preferred for this treatment. In general, an exposure of the metal for one hour to the gas at the preferred temperature will loosen the inner scale so that it can be removed readily by sandblasting or otherwise.

The method of the invention has been found to be satisfactory for the treatment of a great number of steels and alloys. Among those to which the method has been successfully applied are: Carbon steels, chromium steels having from 5% to 25% chromium, 18/8 stainless steel, stainless steel containing titanium or columbium, nickel-base chromium-iron alloys, and chromium-cobalt-tungsten alloys. Excellent results have been obtained with the steels and other alloys containing chromium. If more than about 10% .molybdenum is present in the alloy, the scale formed is often difficult to remove. For this reason, bestresults with molybdenum containing alloys have been obtained with those alloys having a molybdenum content of less than about The rate at which the metal is attacked and the imperfections eliminated depends upon the temperature, composition of the metal being treated, and the thickness of the scale layer present as a result of the treatment. For example, with alloys containing up to 25% chromium, an exposure to hydrogen sulfide at 1000 C. for a period of eight hours will result in the removal of from 0.05 to 0.075 of an inch of metal. At 900 C. and an exposure of two hours to hydrogen sulfide, the same materials will lose from:0.005. to. 0.012 of an inch of metal. In two hours. at 1000: C. these same materials will lose from 0.0 19 to 0.027 of an inch of metal, and at 11.00 0.. with the same time of treatment the loss of metal is from 0.031 to 0.036 of an inch.

The removal of metal can be hastened-byper-iodically removing the loose scale formed. For example, if an .alloysimilar to the one described above is exposed to the hydrogen sulfide for two one-hour periods at 10.00 C; .and the scale is removed after the first. exposure, the. total metal removed is from 0.028 to 0.035 of an inch as compared with 0.019 to 0.0257 of'an inch if the. exposure is for two continuous hours.

The exact time that the alloy is exposed to the gaseous sulfur compound will depend upon the requirements in particular instances. As has been shown above an increase in temperature will in general result in the more rapid removal of metal. However, at temperatures of about 1100 C. and above there is a tendency for the scale to fuse which slows down the action of the sulfur and renders the scale more difficult to remove.

What is claimed is:

1. A process for eliminating surface imperfections from metal which comprises exposing said metal to an atmosphere of a gaseous sulfur compound at a temperature of from 700 C. to 1200 C., effecting the dissociation of the compound to provide sulfur to combine with said metal, maintaining said metal at a temperature of from 700 C. to 1200 C., and subsequently removing from said metal a scale formed on the surface of said metal during said exposure to said gaseous sulfur compound.

2. A process for eliminating surface imperfections from metal which comprises exposing said metal to an atmosphere of a gaseous sulfur compound at a temperature of from 950 C. to 10.50" C., effecting the dissociation. of the comp und to provide sulfur to combine with said, metal, maintaining said metal at a temperature of from 950 C. to 1050 C., and subsequently removing from said metal a scale formed on the surface of said metal during said exposure to said gaseous sulfur compound.

- 3. A process for eliminating surface imperfections from a chromium containing alloy, which process comprises exposing said alloy to an atmosphere of a gaseous, sulfur compound. at a.

temperature of from 850C. to I200 C., effecting the dissociation of. the compound to provide sulfur to combine with saidmeta'l, maintaining saidalloy at a temperature of from 850 C. to 1200 C. to form a loose outer scale and an. adherent inner scale on said alloy, removing, from said alloy the loose outer scale, exposing said alloy with said adherent scale to an atmosphere of a gaseous sulfur compound atv a, temperature. of from 700 C. to 850 C., effecting the dissociationof the compound to provide sulfur to combine. withsaid metal, maintaining said. alloy at. a temperatureof '4 from 700 C. to 850 C. to convert said adherent scale to a loose scale, and removing the latter said loose scale.

4. A process for eliminating surface imperfections from a chromium containing alloy, which process comprises exposing said alloy to anatmosphere ofa gaseous sulfur compound ata temperature of from 950 C. to 1050 C., effecting the dissociation of the compound to provide sulfur to combine, with. said metal, maintaining said alloy at a temperature of from 950 C. to 1050 C. to form a loose outer scale and an adherent inner scale on said alloy, removing from said alloy the loose outer scale, exposing said alloy with said adherent scale to an atmosphere of a gaseous sulfur compound at a temperature of about 800 .elfiecting the dissociation of the compound to provide sulfur to combine with said metal, maintaining said alloy at a temperature of about 800 C. to convert said adherent scale to a loose scale, and removing the latter said'loose scale.

5. A process for eliminating surface imperfections from metal which comprises-exposing said metal to an atmosphere of hydrogen sulfide while maintaining said metal at a temperature of from 700 C. to 1200 C., and subsequently removing from said metal a scale formed on the surface of said metal during said exposure to an atmosphere of hydrogen sulfide.

G. A process according to'cl'aim5" wherein said metal is steel.

7. A process according to-clai-m 5 whenein said metal is an alloy containing-chromium.

S. A process for eliminating surface imperfections from metal which comprises exposing said metal to an atmosphere of hydrogen sulfide while maintaining said metal at a temperature of from 050 C; to 1050 C., and subsequently removing from said metal a scale formed on the surfaceof said metal during said exposure to an atmosmetal is an alloy containing chromium.

11. A process for eliminating surface imperfections from a. chromium containing alloy which process comprises exposing said alloy to an atmosphere of hydrogen sulfide while maintaining said alloy at a temperature of from 850 C. to 12.00" C. to form. a loose outer scale and .an adherent inner scale on .sai'dalloy. removing from. said alloy the loose. outer scale, exposing said al1o y with said adherent scale to. an. atmosphere. of hydrogen sulfide while maintaining said alloy at. a temperature of from, 700 C.. to-8.5.0 C. to convert said adherent scale to a, loose scale, and removing the latter said loose scale.

12-. A process for eliminating surface imperfactions-from achromiumcontaining alloy which process comprises exposing said alloy to. an atmosphere-of hydrogen sulfide while maintainingsaidalloy at a temperature of from 950 C. to l050 C. to form: a loose outer scale and anad-herent inner scalezonsaidalloy, removing from said alloy the loose: outer scale, exposing. said, alloy with said adherent scale. to an. atmosphere of hydrogen sulfide while maintaining-said. alloy ata temperature of about'800" C. to convert said adherent scale to a loose-s.cale,,-and' removing the latter said loose;- scale.

DAKLEY; BINDER.

No. references cited. 

1. A PROCESS FOR ELIMINATING SURFACE IMPERFECTIONS FROM MATERIAL WHICH COMPRISES EXPOSING SAID METAL TO AN ATMOSPHERE OF A GASEOUS SULFUR COMPOUND AT A TEMPERATURE OF FROM 700* C. TO 1200* C., EFFECTING THE DISSOCIATION OF THE COMPOUND TO PROVIDE SULFUR TO COMBINE WITH SAID METAL, MAINTAINING SAID METAL AT A TEMPERATURE OF FROM 700* C. TO 1200* C., AND SUBSEQUENTLY REMOVING FROM SAID METAL A SCALE FORMED ON THE SURFACE OF SAID METAL DURING SAID EXPOSURE TO SAID GASEOUS SULFUR COMPOUND. 